The present invention relates to adjustment devices for adjusting the length of a control cable and more particularly to an adjustment device for adjusting a shifting cable or brake cable for a bicycle.
Control cable adjustment devices are used to adjust the length of a control cable or Bowden cable that connects a gear shifter to a gear change mechanism such as a derailleur or internal gear hub or connects a brake lever to a brake. The control cable includes an inner wire that slides within an outer casing or sheath. The length of the cable needs to be adjusted because elongation of the cable occurs after extended use under load and shifting or braking requires precise cable guidance. Usually the adjustment device is threaded into the shifter or brake housing, resulting in the adjustment device being indirectly braced against the bicycle frame. When the adjustment device is threaded into the housing, the sheath is shortened relative to the inner wire, which then moves loosely in the sheath.
To tighten the control cable, the adjustment device is unscrewed from the housing, resulting in the sheath being elongated relative to the inner wire. Usually the adjustment device includes a locknut or detent mechanism that holds the adjustment device in its current position and also prevents the adjustment device from being rotated in an uncontrolled manner. Various detent mechanisms are shown in U.S. Pat. No. 5,674,142; 4,833,937, EP 0 916 570 A2, and German Utility Model DE-GM 76 26 479.
U.S. Pat. No. 5,674,142 discloses an adjustment device having an elongated retention nut that is threaded onto an elongated mounting member of a shifter housing. The device includes a detent mechanism having detents located on an inner surface of the retention nut that are engageable with protrusions on an outer surface of the mounting member. The protrusions are located adjacent the inner end of the threads on the mounting member. A problem with this configuration is that by arranging the threads and the protrusions adjacent one another, the adjustment device is relatively long.
U.S. Pat. No. 4,833,937 discloses a detent mechanism that includes a disk rotatably connected to the adjuster and having protrusions which is biased by a spring to engage detents located on the outer surface of a stop nonrotatably connected to a shifter housing. When the adjuster is rotated the disk rotates between the protrusions to provide stepwise adjustment of a control cable. A problem with this configuration is that it requires a lot of components and requires a cover for the detent mechanism, which also unnecessarily enlarges the outside diameter of the adjustment device.
In EP 0 916 570 A2, the detent mechanism includes a spring having a first end that is secured in a slot of a brake lever housing and a second end that engages a channel in the outside diameter of the adjuster. After each complete adjustment revolution, the end of the spring element snaps into the channel provided for the control cable on the adjuster. Although this adjustment device has fewer components than the previous mentioned adjustment devices, it requires an additional slot in the brake housing to receive one end of the spring. Another problem with this configuration is that the spring reengages the insertion slot in the adjuster only after each complete revolution of the adjuster, resulting in only coarse control cable adjustment.
The detent mechanism described in DE-GM 76 26 479 generally includes an adjustment nut having external longitudinal flutes and a screw thread that is surrounded by flexible retention arms which engage the longitudinal flutes to provide the detent function. A problem with this configuration is that the externally located flexible retention arms unnecessarily enlarge the outside diameter of the adjustment device and requires a cover to prevent soiling of the detent mechanism. Therefore there is a need for a control cable adjustment device that is compact and has minimal parts.